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Franziska Kopp, Thomas Stahnke, Niels Grabow, Klaus-Peter Schmitz, Rudolf F Guthoff, Stefan Siewert; Development of an evaluation protocol to assess aqueous humor outflow after MIGS procedures. Invest. Ophthalmol. Vis. Sci. 2018;59(9):2710.
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Micro-invasive glaucoma surgery (MIGS) procedures have become an important treatment approach for primary open angle glaucoma. The efficiency of MIGS for aqueous humor drainage has yet to be systematically investigated in long term follow up studies. We are developing an oculo-pression protocol to gain insight into aqueous humor outflow dynamics. Within the current study, we compared two different pressure reducing devices: a straight line pressure reducer (SLPR) with adjustable weights and the Honan pressure reducer (HPR) with regard to their effect on intraocular pressure (IOP) in enucleated porcine eyes.
A 23G cannula, connected to a fluid reservoir with buffered saline solution, was introduced into the vitreous cavity to set baseline pressure to 15.6 ± 0.5 mmHg. For IOP-monitoring, another 23G cannula, connected to a pressure transducer, was inserted into the anterior chamber. The SLPR was positioned on the central cornea and held in place for 5 min. The procedure was performed successively with 200, 300, and 400 g. The HPR was fixed above the cornea and set to 30, 50, and 100 mmHg for 5 minutes, respectively.
The SLPR caused peak IOP values, recorded immediately after SLPR-application, of 126.0 ± 23.4, 173.8 ± 34.7, and 203.3 ± 38.4 mmHg, with a weight of 200, 300, and 400 g, respectively (each n = 3). Subsequent pressure decrease was weight-dependent with the steepest decrease of 0.33 ± 0.08 mmHg /sec observed with 400 g. With the HPR, the chosen pressure values of 30, 50, and 100 mmHg resulted in peak IOP of 57.4 ± 6.9, 78.8 ± 13.0, and 102.2 ± 12 mmHg, respectively (each n = 3). Subsequent IOP decrease was dependent on the HPR value with the steepest decline detected with 100 mmHg.
We are developing an oculo-pression protocol to systematically evaluate aqueous humor outflow dynamics. Our ex vivo measurement setup can easily be transferred to clinical settings with non-invasive Goldman tonometry and is suitable for long term evaluation of aqueous humor outflow facility. Due to easier handling and more precisely adjustable pressure values, the HPR is our favored approach. In future studies the measurements will be performed with healthy and glaucomatous eyes of human subjects, before and after MIGS, to specifically assess the contribution of the implanted drainage device to aqueous humor outflow.
This is an abstract that was submitted for the 2018 ARVO Annual Meeting, held in Honolulu, Hawaii, April 29 - May 3, 2018.
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